Make multisort compatible with Sort

Test code
```php
$orders = $this->getSort()->getOrders();
ArrayHelper::multisort($data, array_keys($orders), array_values($orders));
```

Fixed issue with getting Object component

Fixes #226: atomic operations and transaction support in AR.

RBAC: Item and Assignment optimized save approach

Renamed yiirequirements.php to requirements.php

"YiiRequirementChecker" console view has been reworked to display requirements by blocks and in brief for the successful ones.